A charge pump is an electronic circuit that comprises both a current source and a current sink. Therefore, a charge pump may provide current to, or receive current from an external system. There are many applications in electronics where a charge pump may be utilized. For example, a charge pump is commonly used in a phase lock loop circuit. Such a phase lock loop may be used, for example, in a read channel integrated circuit for a hard disk drive of a computer system.
Existing charge pump circuits and methods exhibit several disadvantages. First, the current source may operate more slowly than the current sink. Therefore, the transient response of the source and sink may not match. Existing current sources are typically fabricated using P-Channel transistors. Parasitic capacitance in the P-Channel transistors may cause the current source to operate more slowly than a current sink fabricated with complementary N-Channel transistors. A charge pump used in, for example, a phase lock loop, may need to have a current source that more closely matches the capabilities of the current sink. If the current source and current sink do not match, the phase lock loop may not operate properly. Finally, existing charge pumps may not provide a stable output current.